package org.apache.lucene.distributed;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.PrintStream;
import java.lang.annotation.Annotation;
import java.net.URL;
import java.net.URLDecoder;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Set;
import java.util.jar.JarEntry;
import java.util.jar.JarInputStream;

/**
 * <p>
 * ResolverUtil is used to locate classes that are available in the/a class path
 * and meet arbitrary conditions. The two most common conditions are that a
 * class implements/extends another class, or that is it annotated with a
 * specific annotation. However, through the use of the {@link Test} class it is
 * possible to search using arbitrary conditions.
 * </p>
 * 
 * <p>
 * A ClassLoader is used to locate all locations (directories and jar files) in
 * the class path that contain classes within certain packages, and then to load
 * those classes and check them. By default the ClassLoader returned by
 * {@code Thread.currentThread().getContextClassLoader()} is used, but this can
 * be overridden by calling {@link #setClassLoader(ClassLoader)} prior to
 * invoking any of the {@code find()} methods.
 * </p>
 * 
 * <p>
 * General searches are initiated by calling the
 * {@link #find(com.opensymphony.xwork2.util.ResolverUtil.Test, String...)} ()}
 * method and supplying a package name and a Test instance. This will cause the
 * named package <b>and all sub-packages</b> to be scanned for classes that
 * meet the test. There are also utility methods for the common use cases of
 * scanning multiple packages for extensions of particular classes, or classes
 * annotated with a specific annotation.
 * </p>
 * 
 * <p>
 * The standard usage pattern for the ResolverUtil class is as follows:
 * </p>
 * 
 * <pre>
 * esolverUtil&lt;ActionBean&gt; resolver = new ResolverUtil&lt;ActionBean&gt;();
 * esolver.findImplementation(ActionBean.class, pkg1, pkg2);
 * esolver.find(new CustomTest(), pkg1);
 * esolver.find(new CustomTest(), pkg2);
 * ollection&lt;ActionBean&gt; beans = resolver.getClasses();
 * </pre>
 * 
 * <p>
 * This class was copied from Stripes -
 * http://stripes.mc4j.org/confluence/display/stripes/Home
 * </p>
 * 
 * @author Tim Fennell
 */
public class ResolverUtil<T> {
  PrintStream ERR = System.err;
  /** An instance of Log to use for logging in this class. */
  //private static final Logger LOG = LoggerFactory.getLogger(ResolverUtil.class);

  /**
   * A simple interface that specifies how to test classes to determine if they
   * are to be included in the results produced by the ResolverUtil.
   */
  public static interface Test {
    /**
     * Will be called repeatedly with candidate classes. Must return True if a
     * class is to be included in the results, false otherwise.
     */
    boolean matches(Class type);

    boolean matches(URL resource);

    boolean doesMatchClass();

    boolean doesMatchResource();
  }

  public static abstract class ClassTest implements Test {
    public boolean matches(URL resource) {
      throw new UnsupportedOperationException();
    }

    public boolean doesMatchClass() {
      return true;
    }

    public boolean doesMatchResource() {
      return false;
    }
  }

  public static abstract class ResourceTest implements Test {
    public boolean matches(Class cls) {
      throw new UnsupportedOperationException();
    }

    public boolean doesMatchClass() {
      return false;
    }

    public boolean doesMatchResource() {
      return true;
    }
  }

  /**
   * A Test that checks to see if each class is assignable to the provided
   * class. Note that this test will match the parent type itself if it is
   * presented for matching.
   */
  public static class IsA extends ClassTest {
    private Class parent;

    /**
     * Constructs an IsA test using the supplied Class as the parent
     * class/interface.
     */
    public IsA(Class parentType) {
      this.parent = parentType;
    }

    /**
     * Returns true if type is assignable to the parent type supplied in the
     * constructor.
     */
    public boolean matches(Class type) {
      return type != null && parent.isAssignableFrom(type);
    }

    @Override
    public String toString() {
      return "is assignable to " + parent.getSimpleName();
    }
  }

  /**
   * A Test that checks to see if each class name ends with the provided suffix.
   */
  public static class NameEndsWith extends ClassTest {
    private String suffix;

    /** Constructs a NameEndsWith test using the supplied suffix. */
    public NameEndsWith(String suffix) {
      this.suffix = suffix;
    }

    /**
     * Returns true if type name ends with the suffix supplied in the
     * constructor.
     */
    public boolean matches(Class type) {
      return type != null && type.getName().endsWith(suffix);
    }

    @Override
    public String toString() {
      return "ends with the suffix " + suffix;
    }
  }

  /**
   * A Test that checks to see if each class is annotated with a specific
   * annotation. If it is, then the test returns true, otherwise false.
   */
  public static class AnnotatedWith extends ClassTest {
    private Class<? extends Annotation> annotation;

    /** Construts an AnnotatedWith test for the specified annotation type. */
    public AnnotatedWith(Class<? extends Annotation> annotation) {
      this.annotation = annotation;
    }

    /**
     * Returns true if the type is annotated with the class provided to the
     * constructor.
     */
    public boolean matches(Class type) {
      return type != null && type.isAnnotationPresent(annotation);
    }

    @Override
    public String toString() {
      return "annotated with @" + annotation.getSimpleName();
    }
  }

  public static class NameIs extends ResourceTest {
    private String name;

    public NameIs(String name) {
      this.name = "/" + name;
    }

    public boolean matches(URL resource) {
      return (resource.getPath().endsWith(name));
    }

    @Override
    public String toString() {
      return "named " + name;
    }
  }

  /** The set of matches being accumulated. */
  private Set<Class<? extends T>> classMatches = new HashSet<Class<? extends T>>();

  /** The set of matches being accumulated. */
  private Set<URL> resourceMatches = new HashSet<URL>();

  /**
   * The ClassLoader to use when looking for classes. If null then the
   * ClassLoader returned by Thread.currentThread().getContextClassLoader() will
   * be used.
   */
  private ClassLoader classloader;

  /**
   * Provides access to the classes discovered so far. If no calls have been
   * made to any of the {@code find()} methods, this set will be empty.
   * 
   * @return the set of classes that have been discovered.
   */
  public Set<Class<? extends T>> getClasses() {
    return classMatches;
  }

  public Set<URL> getResources() {
    return resourceMatches;
  }

  /**
   * Returns the classloader that will be used for scanning for classes. If no
   * explicit ClassLoader has been set by the calling, the context class loader
   * will be used.
   * 
   * @return the ClassLoader that will be used to scan for classes
   */
  public ClassLoader getClassLoader() {
    return classloader == null ? Thread.currentThread().getContextClassLoader() : classloader;
  }

  /**
   * Sets an explicit ClassLoader that should be used when scanning for classes.
   * If none is set then the context classloader will be used.
   * 
   * @param classloader
   *          a ClassLoader to use when scanning for classes
   */
  public void setClassLoader(ClassLoader classloader) {
    this.classloader = classloader;
  }

  /**
   * Attempts to discover classes that are assignable to the type provided. In
   * the case that an interface is provided this method will collect
   * implementations. In the case of a non-interface class, subclasses will be
   * collected. Accumulated classes can be accessed by calling
   * {@link #getClasses()}.
   * 
   * @param parent
   *          the class of interface to find subclasses or implementations of
   * @param packageNames
   *          one or more package names to scan (including subpackages) for
   *          classes
   */
  public void findImplementations(Class parent, String... packageNames) {
    if (packageNames == null)
      return;

    Test test = new IsA(parent);
    for (String pkg : packageNames) {
      findInPackage(test, pkg);
    }
  }

  /**
   * Attempts to discover classes who's name ends with the provided suffix.
   * Accumulated classes can be accessed by calling {@link #getClasses()}.
   * 
   * @param suffix
   *          The class name suffix to match
   * @param packageNames
   *          one or more package names to scan (including subpackages) for
   *          classes
   */
  public void findSuffix(String suffix, String... packageNames) {
    if (packageNames == null)
      return;

    Test test = new NameEndsWith(suffix);
    for (String pkg : packageNames) {
      findInPackage(test, pkg);
    }
  }

  /**
   * Attempts to discover classes that are annotated with to the annotation.
   * Accumulated classes can be accessed by calling {@link #getClasses()}.
   * 
   * @param annotation
   *          the annotation that should be present on matching classes
   * @param packageNames
   *          one or more package names to scan (including subpackages) for
   *          classes
   */
  public void findAnnotated(Class<? extends Annotation> annotation, String... packageNames) {
    if (packageNames == null)
      return;

    Test test = new AnnotatedWith(annotation);
    for (String pkg : packageNames) {
      findInPackage(test, pkg);
    }
  }

  public void findNamedResource(String name, String... pathNames) {
    if (pathNames == null)
      return;

    Test test = new NameIs(name);
    for (String pkg : pathNames) {
      findInPackage(test, pkg);
    }
  }

  /**
   * Attempts to discover classes that pass the test. Accumulated classes can be
   * accessed by calling {@link #getClasses()}.
   * 
   * @param test
   *          the test to determine matching classes
   * @param packageNames
   *          one or more package names to scan (including subpackages) for
   *          classes
   */
  public void find(Test test, String... packageNames) {
    if (packageNames == null)
      return;

    for (String pkg : packageNames) {
      findInPackage(test, pkg);
    }
  }

  /**
   * Scans for classes starting at the package provided and descending into
   * subpackages. Each class is offered up to the Test as it is discovered, and
   * if the Test returns true the class is retained. Accumulated classes can be
   * fetched by calling {@link #getClasses()}.
   * 
   * @param test
   *          an instance of {@link Test} that will be used to filter classes
   * @param packageName
   *          the name of the package from which to start scanning for classes,
   *          e.g. {@code net.sourceforge.stripes}
   */
  public void findInPackage(Test test, String packageName) {
    packageName = packageName.replace('.', '/');
    ClassLoader loader = getClassLoader();
    Enumeration<URL> urls;

    try {
      urls = loader.getResources(packageName);
    } catch (IOException ioe) {
      ERR.println("Could not read package: " + packageName);
      return;
    }

    while (urls.hasMoreElements()) {
      try {
        String urlPath = urls.nextElement().getFile();
        urlPath = URLDecoder.decode(urlPath, "UTF-8");

        // If it's a file in a directory, trim the stupid file: spec
        if (urlPath.startsWith("file:")) {
          urlPath = urlPath.substring(5);
        }

        // Else it's in a JAR, grab the path to the jar
        if (urlPath.indexOf('!') > 0) {
          urlPath = urlPath.substring(0, urlPath.indexOf('!'));
        }

        ERR.println("Scanning for classes in [" + urlPath + "] matching criteria: " + test);
        File file = new File(urlPath);
        if (file.isDirectory()) {
          loadImplementationsInDirectory(test, packageName, file);
        } else {
          loadImplementationsInJar(test, packageName, file);
        }
      } catch (IOException ioe) {
        ERR.println("could not read entries");
      }
    }
  }

  /**
   * Finds matches in a physical directory on a filesystem. Examines all files
   * within a directory - if the File object is not a directory, and ends with
   * <i>.class</i> the file is loaded and tested to see if it is acceptable
   * according to the Test. Operates recursively to find classes within a folder
   * structure matching the package structure.
   * 
   * @param test
   *          a Test used to filter the classes that are discovered
   * @param parent
   *          the package name up to this directory in the package hierarchy.
   *          E.g. if /classes is in the classpath and we wish to examine files
   *          in /classes/org/apache then the values of <i>parent</i> would be
   *          <i>org/apache</i>
   * @param location
   *          a File object representing a directory
   */
  private void loadImplementationsInDirectory(Test test, String parent, File location) {
    File[] files = location.listFiles();
    StringBuilder builder = null;

    for (File file : files) {
      builder = new StringBuilder(100);
      builder.append(parent).append("/").append(file.getName());
      String packageOrClass = (parent == null ? file.getName() : builder.toString());

      if (file.isDirectory()) {
        loadImplementationsInDirectory(test, packageOrClass, file);
      } else if (isTestApplicable(test, file.getName())) {
        addIfMatching(test, packageOrClass);
      }
    }
  }

  private boolean isTestApplicable(Test test, String path) {
    return test.doesMatchResource() || path.endsWith(".class") && test.doesMatchClass();
  }

  /**
   * Finds matching classes within a jar files that contains a folder structure
   * matching the package structure. If the File is not a JarFile or does not
   * exist a warning will be logged, but no error will be raised.
   * 
   * @param test
   *          a Test used to filter the classes that are discovered
   * @param parent
   *          the parent package under which classes must be in order to be
   *          considered
   * @param jarfile
   *          the jar file to be examined for classes
   */
  private void loadImplementationsInJar(Test test, String parent, File jarfile) {

    try {
      JarEntry entry;
      JarInputStream jarStream = new JarInputStream(new FileInputStream(jarfile));

      while ((entry = jarStream.getNextJarEntry()) != null) {
        String name = entry.getName();
        if (!entry.isDirectory() && name.startsWith(parent) && isTestApplicable(test, name)) {
          addIfMatching(test, name);
        }
      }
    } catch (IOException ioe) {
      ERR.println("Could not search jar file '" + jarfile + "' for classes matching criteria: " + test + " due to an IOException");
    }
  }

  /**
   * Add the class designated by the fully qualified class name provided to the
   * set of resolved classes if and only if it is approved by the Test supplied.
   * 
   * @param test
   *          the test used to determine if the class matches
   * @param fqn
   *          the fully qualified name of a class
   */
  protected void addIfMatching(Test test, String fqn) {
    try {
      ClassLoader loader = getClassLoader();
      if (test.doesMatchClass()) {
        String externalName = fqn.substring(0, fqn.indexOf('.')).replace('/', '.');
        //if (LOG.isDebugEnabled()) {
        ERR.println("Checking to see if class " + externalName + " matches criteria [" + test + "]");
        //}
        if (externalName.startsWith(".")) {
          externalName = externalName.substring(1, externalName.length());
        }
        Class type = loader.loadClass(externalName);
        if (test.matches(type)) {
          classMatches.add((Class<T>) type);
        }
      }
      if (test.doesMatchResource()) {
        URL url = loader.getResource(fqn);
        if (url == null) {
          url = loader.getResource(fqn.substring(1));
        }
        if (url != null && test.matches(url)) {
          resourceMatches.add(url);
        }
      }
    } catch (Throwable t) {
      ERR.println("Could not examine class '" + fqn + "' due to a " + t.getClass().getName() + " with message: " + t.getMessage());
    }
  }
}